1. Field of the Invention
This invention relates to the protection of gamma titanium aluminide alloy structures and more particularly to protective coatings for such structures.
2. Description of the Related Art
Titanium aluminide intermetallics are attractive for use in advanced structural applications such as aircraft systems, because they offer a desirable combination of low density and high temperature strength. At high temperatures, however, titanium aluminides presently have very limited use because of their poor oxidation resistance.
U.S. Pat. No. 4,369,233, issued to Teunis van Schaik, entitled "Process to Apply a Protecting Silicon Containing Coating On Specimen Produced From Superalloys and Product", discloses a corrosion resistant coating for use on a super alloy substrate (a nickel based alloy). The silicon coating is comprised of Ti.sub.6 Si.sub.7 Ni.sub.16. The Ti layer is applied by ion plating. It is diffused in the super alloy and a Si layer is applied by a pack coat process.
U.S. Pat. No. 2,467,114, issued to A. J. Deyrup, entitled "Vitreous Coatings For Light Metals", discloses use of a coating, primarily comprised of PbO, SiO.sub.2, and Li.sub.2 O, on aluminum and aluminum rich alloys.
U.S. Pat. No. 3,698,943, issued to W. R. Colantuono, entitled "Protective Coating", discloses use of a protective coating for hot metal workpieces, particularly high-speed tool steels. The coating consists of sodium borate, silica and a viscosity-promoting agent, such as alumina.